Chapter 21: Digestive System Study Guide

Define: bolus and chyme

- Bolus: a small rounded mass of chewed food during swallowing. - Chyme: a semifluid paste that is produced when the mixing of food in the stomach w/ gastric juice occurs.

The gastric cells secrete which substances?

- Chief cells: 1. pepsinogen 2. gastric lipase - Parietal cells 1. intrinsic factor 2. hydrochloric acid

What are the functions of the secretions: HCl, mucous, pepsinogen, intrinsic factor

- HCl: needed to convert pepsinogen to pepsin (secreted from parietal cells). - mucous: protective to stomach wall (secreted from goblet cells). - pepsinogen: inactive form of pepsin (secreted from chief cells). - intrinsic factor: required for vitamin B12 absorption (secreted from parietal cells).

Describe the structure of the stomach. What 4 parts make up the stomach? Define rugae and explain the importance of muscle arrangement.

- J-shaped, pouch-like organ that is about 25-30 cm long. - hangs inferior to diaphragm in the upper-left portion of abdominal cavity. - has 3 layers of smooth muscle: an inner circular layer, and outer longitudinal layer, and possibly a middle third oblique layer. - has 4 parts: 1. Cardia (surrounds cardial orifice) 2. Fondus (dome-shaped region beneath) 3. Body (midportion) 4. Pyloric region (pyloric sphincter) - Rugae: folds of mucosa and submucosa to allow for distension. - Muscle arrangement & importance: the stomach has an internal, middle, and external layer of muscle fibers that physically help to churn food during digestion.

Define segmentation and peristalsis. Where do they occur?

- Peristalsis: moves food through the esophagus to the stomach; pushing movements that propel chyme; (this occurs in the esophagus, stomach, SI, LI). - Segmentation: ring-like contractions that can move chyme back and forth; food mixing & slow propulsion (this occurs in the SI).

How do hormones secretin & CCK affect pancreatic and bile secretion regulation?

- Secretin: stimulates pancreas to release pancreatic juice high in bicarbonate ions; bile salts and, to a lesser extent, secretin transported via bloodstream stimulate Liver to produce bile more rapidly. - Cholecystokinin (CCK): stimulates pancreas to release pancreatic juice high in enzymes; stimulates gallbladder contraction when exposed to acidic fatty chyme, causes vagal stimulation, and hepatopancreatic sphincter to relax; this allows bile to enter duodenum.

Where are carbohydrates, proteins, nucleic acids, and lipids broken down?

- carbohydrates: digestion starts in mouth when salivary amylase starts to break down starch, and then broken down in duodenum of SI by pancreatic amylase. - proteins: broken down in the stomach by pepsin. - nucleic acids: broken down by nucleases in SI. - lipids: broken down by bile slats in the lumen of the digestive tract (of SI).

What are the functions of the small intestine?

- completes digestion of nutrients in chyme. - absorbs products of digestion. - transports the remaining residue to the large intestine. - small intestinal wall increases SA of proximal part for nutrient absorption.

What is the composition of pancreatic juice? What does each enzyme break down?

- contains digestive enzymes and bicarbonate ions that help digest carbohydrates, proteins, fats, and nucleic acids. - Lipase: breaks down triglycerides. - Amylase: splits glycogen into disaccharides. - Trypsin: digests proteins (releases inactive trypsinogen; activated by enterokinase). - Chymotrypsin: digests proteins (activated by trypsin). - Carboxypeptidase: digests proteins (activated by trypsin). - Nucleases: digests nucleic acids. - Bicarbonate ions: makes pancreatic juice alkaline.

What are the functions of the SI hormones?

- enterokinase: converts trypsinogen to trypsin. - somatostatin: inhibits acid secretion by stomach. - CCK: inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, and stimulates gallbladder to release bile. - secretin: stimulates pancreas to release bicarbonate ions in pancreas juice.

What are the functions of the accessory organs?

- overall, they empty into the alimentary canal. - teeth: grind down food into smaller pieces. - tongue: helps w/ swallowing food, papillae help grip food. - salivary glands: produce saliva and begin digestion of carbohydrates. - liver: produces bile. - gallbladder: stores/recycles bile. - pancreas: secretes digestive enzymes into small intestine.

What are the functions of the small intestinal secretions?

- peptidase: breaks down peptides into amino acids. - sucrase/maltase/lactase: break down disaccharides into monosaccharides. - lipase: break down fats into fatty acids and glycerol.

Where are the locations of the pyloric valve and ileocecal sphincter?

- pyloric valve is the sphincter controlling stomach emptying, located at the pylorus of the stomach. - ileocecal sphincter joins the SI and LI (colon).

Describe the digestive enzymes: salivary amylase, pepsin, gastric lipase

- salivary amylase: splits starch into disaccharides (found in saliva of mouth). - pepsin: protein splitting enzyme; comes from pepsinogen in presence of HCl acid (found in stomach). - gastric lipase: fat splitting; comes from chief cells; weak due to low pH; breaks down fats into fatty acids and glycerol (found in stomach; secreted by SI).

What are the functions of the large intestine?

- segmental mixing - mass movement for propulsion - secretes mucus (goblet cells) - absorbs ions, water, minerals, electrolytes, vitamins, and small organic molecules produced by bacteria. - houses intestinal flora: vitamin Bs, K - forms feces and carries out defecation

Define digestion and include the 6 essential activities

- the mechanical and chemical breakdown of foods into forms that cell membranes can absorb. 1. ingestion 2. propulsion 3. mechanical breakdown 4. digestion 5. absorption 6. defecation

Describe the 3 phases of gastric secretion

1. Cephalic Phase: the sight, smell, taste, or thought of food triggers parasympathetic reflexes; gastric juice is secreted in response. 2. Gastric Phase: food in stomach chemically and mechanically stimulates release of gastrin, which in turn, stimulates secretion of gastric juice; reflect response also stimulates gastric juice secretion. 3. Intestinal Phase: as food enters the SI, it stimulates intestinal cells to release intestinal gastrin, which briefly promotes the secretion of gastric juice from stomach wall. This phase primarily inhibits gastric juice secretion.

How is bile and pancreatic juice regulated?

1. Chyme entering duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin. 2. CCK and secretin enter the bloodstream. 3. CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3− rich pancreatic juice. 4. Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate Liver to produce bile more rapidly. 5. CCK (via blood stream) causes gallbladder to contract and Hepatopancreatic Sphincter to relax. Bile Enters duodenum. 6. During cephalic and gastric phases, vagal Nerve stimulates gallbladder to contract weakly.

What are the 3 sections of the small intestine?

1. Duodenum 2. Jejunum 3. Ileum

Extra Credit Question: What are the 4 types of teeth?

1. Incisors 2. Canines 3. Premolars 4. Molars

Describe the functions of pancreatic enzymes.

1. Lipase - breaks down triglycerides. 2. Amylase - splits glycogen into disaccharides. 3. Trypsin - digests proteins (releases inactive trypsinogen; activated by enterokinase). 4. Chymotrypsin - digests proteins (activated by trypsin). 5. Carboxypeptidase - digests proteins (activated by trypsin). 6. Nucleases - digits nucleic acids. 7. Bicarbonate ions - makes pancreatic juice alkaline.

List the Digestive organs (in correct order)

1. Mouth (includes salivary glands, tongue) 2. Pharynx 3. Esophagus 4. Stomach 5. **Liver & Gallbladder** 6. Small intestine (w/ duodenum, jejunum, ileum) 7. **Pancreas** 8. Large Intestine (w/ transverse colon, descending & ascending colon, cecum, sigmoid colon, rectum, and appendix) 9. Anus

Identify the characteristics & functions of the 4 layers of the digestive wall? Place them in order.

1. Mucosa: innermost layer made of simple columnar epithelium; lines GI tract and provides vascular support for epithelium. 2. Submucosa: lies underneath the mucosa and made of loose CT; contains blood vessels. nerve plexuses and mucus secreting glands. 3. Muscularis Externa: smooth muscle layer; helps move food down through the gut by peristalsis. 4. Serosa: outermost layer made of loose CT; contains blood vessels & secretes serous peritoneal fluid.

How are small intestinal secretions regulated?

1. Mucus secretion is stimulated by the presence of chyme in the SI. 2. Distention of the intestinal wall activates nerve plexuses in the wall of SI. 3. Parasympathetic reflexes triggers release of intestinal enzymes.

What are the 3 salivary glands? What composes saliva? Functions?

1. Parotid 2. Submandibular 3. Sublingual - saliva is composed of: 98% water, mucus, proteins, mineral salts, amylase, hydrogen ions, Ca2+ ions, and inorganic phosphate. - saliva works to: cleanse the mouth, dissolve food chemicals for taste, moisten food and compact it into a bolus, and begin the breakdown of starch w/ enzymes.

Describe the steps of swallowing

1. Voluntary stage where saliva is mixed with chewed food, forming a bolus. 2. Swallowing begins and the swallowing reflex is triggered: • the palate and uvula raise • the hyoid bone and larynx elevate • the epiglottis closes off top of the trachea • the longitudinal muscles of pharynx contract • the inferior constrictor muscles relax and the esophagus opens • the peristaltic waves pushes food through the pharynx 3. Peristalsis transports bolus in the esophagus to the stomach.

Describe the functions of the liver.

1. produces glycogen from glucose. 2. breaks down glycogen into glucose. 3. converts non-carbohydrates to glucose. 4. oxidizes fatty acids. 5. forms urea. 6. acts as a blood reservoir. 7. synthesizes plasma proteins. 8. converts carbs and protein to fat. 9. converts amino acids to other amino acids. ~~ It receives 25% of Cardiac Output

What 4 substances can the stomach absorb?

1. some water 2. certain salts 3. certain lipid-soluble drugs 4. alcohol

Describe the composition of bile and know its functions

Bile contains: - water - bile salts (that emulsify fats, absorb fatty acids, cholesterol, and fat-soluble vitamins) - bile pigments (bilirubin & biliverdin) - cholesterol - electrolytes - They work to increase absorption of fats.

Absorption of Small Intestine

Small intestine absorption is so effective that very little absorbable material reaches the organ's distal end.

Which hormones affect gastric secretion and how?

Somatostatin: inhibits acid secretion. CCK: (released by SI cells when proteins & fats enter SI) decreases gastric motility. Gastrin: increases gastric juice secretion.